Contamination of liquid streams with various organic and inorganic pollutants is a serious global environmental problem affecting environment quality and represents significant threat to human health and safety. Substantial metal contamination of aquatic environments may arise from current or past commercial mining and metal extraction processes, surfaces modification and protection processes, or communal and industrial waste sites resulting from a variety of active or defunct industrial fabrication and manufacturing activities. Similarly, significant organic water pollutants, like aliphatic, aromatic, or halogenated hydrocarbons and phenols are frequently associated with oil exploration, extraction and refining, chemicals production, manufacturing processes, or large-scale farming and food processing.
In addition to potential for significant environmental damage, polluted liquid streams represent dilute sources of desirable raw materials like heavy metals and metal oxides. For example, the Berkeley Mine Pit in Butte, Mont. alone represents an estimated 30 billion gallons of acid mine drainage which contains 180 ppm of copper along with other metals and thus could yield up to 22,000 tons of pure copper by use of a small treatment facility.
An economically relevant group of prior art methods of removal of heavy metal ions from liquid solutions is based on chemical precipitation. This process is generally burdened by complexity, high cost, clear preference for extremely large facilities and high-volume operations. Lime neutralization may be regarded as a dominant treatment approach. In general, several embodiments of this approach may yield byproducts including precipitated sludge which may become a concentrated yet mixed contaminant source of the toxins in the source material. The sludge mandates further processing and costly long term disposal as a hazardous waste. Many similar disadvantages burden alternative heavy ion removal methods that may incorporate: filtration, ion exchange, foam generation and separation, reverse osmosis, or combinations of listed processes.
Considerable market research conducted by many strategic metal mining and extraction industry consultants indicates that high grade ore reserves are becoming exhausted, leading world-wide to generally downward trending ore quality. For example, practitioners may need a way to use their existing recovery equipment and processes to recover metals from their often plentiful but presently unusable low-grade ore or tailings from legacy operations. Currently, mines may not be capable to economically process metals when ore sources and/or the resultant process streams containing the target metal extracted from these ores are too weak and need strengthening (concentrating) to allow practical conventional target metal extraction. Thus, the economic considerations may be closely coupled with technology limitations providing for continuous motivation to improve all aspects of the extraction process as measured by cost (capital and operational) reduction metrics.
The extraction technologies enabled by several aspects of the current invention may be adapted to address at least some of the above considerations. In general, metal extraction methods based on redox reactions frequently require acidity control and pH manipulation (such as lowering pH to refresh acid for processing streams, raising pH to improve processing and/or controllably (and selectively) drop out contaminants (metals) as valuable products (hydroxides or other pH sensitive precipitates), or (potentially in conjunction with pH adjust via counter reaction)—manipulate target species redox states to improve selected aspects of the target stream processing. Classic examples may incorporate but are not limited to conversions of Fe+3 to Fe+2, Fe+2 to Fe+3, or Cu+1 to Cu+2 and Cu+2 to Cu+1.
In particular, technologies for capture of mined metals (e.g. copper processing) from streams frequently include modification of mining streams (raffinate, wastewater, draindown, processing bleeds, Pregnant Leach Solution (PLS), and other stream's chemistry to improve mining productivity. The invention here affords a new ability to effect and control such modifications electrochemically to improve processing efficiency and/or operations.
Mining influenced waters like Acid Rock Drainage (ARD) and acid or alkaline leachates (essentially a naturally occurring leach solution, typically considered wastewater) is often acidic or alkaline and may contain multiple metals in a high sulfate background. ARD could also be economically treated using electrochemical methods of the current invention while achieving new control and selectivity over solids generation during treatment.
Even more particularly, the new method could be employed to perform or mitigate a number of economically relevant treatments traditionally accomplished by chemical additions or needs. Nonexclusive examples include increases of acidity (lower pH) and/or increase of Fe+3 concentrations (e.g. for sulfide leaching) which may enhance leaching processes. Similarly, one may lower acidity (raise pH) to enhance solvent extraction efficiency or neutralize streams with potential selective metal (hydroxide) recovery, or one could lower Fe+3 content (e.g. converting it to Fe+2), to increase the pH of solids formation (precipitation) (e.g. to avoid scale formation/fouling and/or allow selective removal), and effect selectivity/efficiency of other processes like solvent extraction or ion exchange.
Even further, various methods of the electrochemical pH adjustment may be utilized in embodiments concerning control of microbial (viral, bacterial, fungal, protozoal, and macromolecular including misfolded proteins and other malformed molecules, prions and fungal prions) infestations. Usage of acidic or alkaline conditions for control, destruction, sterilization, and or inactivation of microbiological agents has been well understood by practitioners. In particular embodiments of the current inventions, electrochemically generated acidic or alkaline ions may be used to facilitate effectiveness of added or in-situ generated biocides and bio-suppressors in addition to being biocidal or bio-suppressive by itself.
Generally, electrochemical apparatus and methods in accordance to the current inventions utilize electricity as convenient, easily-transportable, and efficiently-controllable “universal electrochemical agent” used in the desirable electrochemical reactions (in addition to conventional usage of electricity only as energy supply). Furthermore, in contrast to standard precipitation and pH control processes requiring deliveries of significant amounts of acids, alkalis, and/or salts (e.g. lime or caustic treatments) various embodiments of the current inventions enable reduction of disposable byproducts (e.g. by in-situ recycling and regeneration of desirable components), and flexibility of process optimization achievable, for example, by active real time (continuous or batch-to-batch) controlling of concentrations, flows, efficiencies, and reaction rates of redox reactions in the targeted electrochemical cells.